1. Field of the Invention
This invention relates to a ferroelectric liquid crystal device and more particularly to a ferroelectric liquid crystal device which comprises substrates, voltage applying means, an orientation control layer and a ferroelectric liquid crystal composition layer and is usable as a liquid crystal shutter, a liquid crystal display device or the like.
2. Description of the Related Art
Liquid crystal display devices most widely used at present are those utilizing nematic phase, but they have a drawback such that a display of large capacity such as of 2,000.times.2,000 lines is hard to realize. Specifically, in ordinary twisted nematic (TN) type liquid crystal display devices, contrast decreases as the number of lines increases, so that it is nearly impossible in practice to produce a display device of large capacity such as of 2,000.times.2,000 lines, with a good appearance.
In order to eliminate the drawback of the TN type liquid crystal display devices, liquid crystal display devices of super twisted nematic (STN) type and double super twisted nematic (DSTN) type have been developed. However, they also have a drawback such that contrast and response speed decrease as the number of lines increases. Therefore, it is presently the utmost level that such display devices be provided with a display capacity of approximately 480.times.1920 lines.
On the other hand, there has been also developed a liquid crystal display device of active matrix type where thin film transistors (TFT) are arranged on a substrate, whereby a large capacity display of 1,000.times.1,000 lines and the like can be realized technically. However, the device has a drawback such that its production process takes a longer time with poor yield, leading to a very high production cost.
A means to solve the problems described above, a ferroelectric liquid crystal display device, which is proposed as a liquid crystal display based on a principle different from that for the TN type display device, has been expected to be promising (See N. A. Clark, et al, Appl. Phys, Lett., 36, 899 (1980)). In such a display device, a ferroelectric liquid crystal capable of exhibiting chiral smectic C phase, chiral smetic I phase, etc. is utilized. Because the principle of the device is classified in a type utilizing memory characteristics of the liquid crystal, a larger display capacity may potentially be realized if response speed improves. Because the process does not require an active element such as thin film transistor, the cost for producing the liquid crystal device may not rise.
Furthermore, the ferroelectric liquid crystal device has also a merit of a wide view angle, so that it is considered promising as a device for a display of a larger capacity of 2,000.times.2,000 lines.
Liquid crystal materials used in a ferroelectric liquid crystal display device utilizing the smectic C phase abovesaid is required to exhibit smectic C phase within a wide temperature range of which center is around room temperature. The liquid crystal materials is also required to satisfy various conditions such as high speed response as a device property for realizing a larger capacity display at the first. In this regard, liquid crystal materials are to show large spontaneous polarization and lower viscosity. Furthermore, possessing phase sequence such as IAC (Isotropic-Smectic A-Smectic C) or INAC (Isotropic-Nematic-Smectic A-Smectic C) is required in order to obtain good orientation and bistability when the ferroelectric liquid crystal is applied to a liquid crystal cell, which also requires that a spiral pitch of nematic phase and smectic C phase be sufficiently longer than the thickness of cell. Also, possessing a large tilt angle is needed in order to improve contract and brightness in liquid crystal display.
However, it is impossible at present to satisfy all of such requirements with a single compound. Therefore, a plurality of compounds are mixed together and practically applied as a liquid crystal composition but a sufficiently satisfying liquid crystal composition has not yet been realized. For producing a liquid crystal composition which satisfies practically usable requirements, many single liquid crystal compounds having various properties are to be used in combination and it may require as a content of liquid crystal composition a compound without showing any liquid crystal phase.